FAQ: Prader-Willi Syndrome
Prader-Willi Syndrome (PWS) is the most common known genetic cause of life-threatening obesity in children. Although the cause is complex it results from an abnormality on the 15th chromosome. It occurs in males and females equally and in all races. Prevalence estimates have ranged from 1:8,000 to 1:25,000 with the most likely figure being 1:15,000. PWS typically causes low muscle tone, short stature if not treated with growth hormone, incomplete sexual development, motor and social development delays and a chronic feeling of hunger that, coupled with a metabolism that utilizes drastically fewer calories than normal, can lead to excessive eating and life-threatening obesity. The food compulsion makes constant supervision necessary. Children with PWS can be sweet and loving, but they display characteristics of the Prader-Willi personality that can cause social and behavioral problems. They also have many complex and unique medical issues. With knowledge, support and understanding, persons with PWS can and do become valued members in our communities. They need to be supported by parents, care givers and professionals who have the knowledge and tools needed to assist them in doing this. PWSA of Michigan provides a variety of services to make this possible.
Suspicion of the diagnosis is first assessed clinically, then confirmed by specialized genetic testing on a blood sample. Formal diagnostic criteria for the clinical recognition of PWS have been published (Holm et al, 1993), as have laboratory testing guidelines for PWS (ASHG, 1996).
Early diagnosis of Prader-Willi Syndrome gives parents time to learn about and prepare for the challenges that lie ahead and to establish family routines that will support their child’s diet and behavior needs from the start. Knowing the cause of their child’s developmental delays can facilitate a family’s access to important early intervention services and may help program staff identify areas of specific need or risk. Additionally, a diagnosis of PWS opens the doors to a network of information and support from professionals and other families who are dealing with the syndrome.
It is estimated that one in 12,000 to 15,000 people has PWS. Although considered a “rare” disorder, Prader-Willi Syndrome (PWS) is one of the most common conditions seen in genetics clinics and is the most common genetic cause of obesity that has been identified. PWS is found in people of both sexes and all races.
No. In fact, newborns with PWS often cannot get enough nourishment because low muscle tone impairs their sucking ability. Many require special feeding techniques or tube feeding for several months after birth, until muscle control improves. Sometime in the following years, usually before school age, children with PWS develop an intense interest in food and can quickly gain excess weight if calories are not restricted.
Unfortunately, no appetite suppressant has worked consistently for people with PWS, but there are currently some promising drug studies. Most require an extremely low-calorie diet all their lives and must have their environment designed so that they have very limited access to food. For example, many families have to lock the kitchen or the cabinets and refrigerator. As adults, most affected individuals can control their weight best in a supportive living home designed specifically for people with PWS, where food access can be restricted without interfering with the rights of those who don’t need such restriction.
Most cases of Prader-Willi Syndrome are attributed to a spontaneous genetic error that occurs at or near the time of conception for unknown reasons. In a very small percentage of cases (2 percent or less), a genetic mutation that does not affect the parent is passed on to the child, and in these families more than one child may be affected. A Prader-Willi Syndrome-like disorder can also be acquired after birth if the hypothalamic portion of the brain is damaged through injury or surgery. All families with a child diagnosed with Prader-Willi Syndromeshould see a geneticist for genetic counseling in order to fully understand their chances of having another child with Prader-Willi Syndrome.
Basically, the occurrence of PWS is due to lack of several genes on one of an individual’s two chromosome 15s— the one normally contributed by the father. In the majority of cases, there is a deletion—the critical genes are somehow lost from the chromosome. In most of the remaining cases, the entire chromosome from the father is missing and there are instead two chromosome 15s from the mother (uniparental disomy). The critical paternal genes lacking in people with PWS have a role in the regulation of appetite. This is an area of active research in a number of laboratories around the world, since understanding this defect may be very helpful not only to those with PWS but to understanding obesity in otherwise normal people.
People with Prader-Willi Syndrome have a flaw in the hypothalamus part of their brain, which normally registers feelings of hunger and satiety. While the problem is not yet fully understood, it is apparent that people with this flaw never feel full; they have a continuous urge to eat that they cannot learn to control. To compound this problem, people with Prader-Willi Syndrome need less food than their peers without the syndrome because their bodies have less muscle and tend to burn fewer calories.
In addition to their involuntary focus on food, people with Prader-Willi Syndrome tend to have obsessive/compulsive behaviors that are not related to food, such as repetitive thoughts and verbalizations, collecting and hoarding of possessions, picking at skin irritations, and a strong need for routine and predictability. Frustration or changes in plans can easily set off a loss of emotional control in someone with Prader-Willi Syndrome, ranging from tears to temper tantrums to physical aggression. While psychotropic medications can help some individuals, the essential strategies for minimizing difficult behaviors in Prader-Willi Syndromeare careful structuring of the person’s environment and consistent use of positive behavior management and support.
With help, people with Prader-Willi Syndrome can expect to accomplish many of the things their “normal” peers do—complete school, achieve in their outside areas of interest, be successfully employed, even move away from their family home. They do, however, need a significant amount of support from their families and from school, work, and residential service providers to both achieve these goals and avoid obesity and the serious health consequences that accompany it. Even those with IQs in the normal range need lifelong diet supervision and protection from food availability.